The present invention relates to a developing device used in an electrophotographic-type image forming apparatus such as a copying machine, a printer, and a facsimile, and relates to a charging method used therefor and a printing apparatus having the developing device.
Generally, an electrophotographic-type image forming apparatus (electrophotographic apparatus) such as a copying machine, a printer, and a facsimile includes an LSU, a photoreceptor drum, and a developing device. Here, the LSU is to irradiate laser beam on a rotating photoreceptor drum, and to form an electrostatic latent image on a surface of the photoreceptor drum. Further, a developing device develops (visualizes) the electrostatic latent image by providing toner to the photoreceptor drum.
The developing device includes a developing roller which is provided so as to be adjacent and opposite to the photoreceptor drum. Further, the developing device is set to be capable of providing toner sequentially to the whole electrostatic latent image on the photoreceptor drum by providing toner to the surface of the developing roller and rotating the developing roller in a direction opposite to the photoreceptor drum.
Incidentally, in the above-mentioned developing device, toner is electrostatically absorbed in the electrostatic latent image on the photoreceptor drum, so that developing is performed. Thus, it is required to charge toner by any method.
For example, a developing device using toner of nonmagnetic 1 component system or toner of magnetic 1 component system (toner containing magnetic powder) includes a supplying roller provided opposite to the developing roller, and a layer thickness restricting blade (blade) provided on the downstream side with respect to the supplying roller (on the downstream side along a rolling direction of the developing roller).
The supplying roller supplies toner sequentially to a surface of the rotating developing roller, and the blade restricts a thickness of toner whose surface is uneven on the developing roller. Further, the blade is also charging means, and is set to give frictional charge to toner by rubbing against the toner which serves as charged means. Thus, it is possible to charge toner used to develop images.
A developing device using developer of 2 component system, in which carrier is mixed with toner, is arranged so that toner and carrier are stirred and mixed in a toner tank, and friction which occurs between them gives frictional charge to the toner as in the foregoing manner. In this case, the carrier serves as the charging means.
However, according to the arrangement in which friction against the blade (mechanical friction) charges toner, it is required to enlarge speed difference between the toner and the blade so as to obtain a sufficient amount of charge. While, mechanical/thermal load is given to the toner and the blade in proportion to the speed difference.
Thus, if the speed difference is enlarged so as to obtain the sufficient amount of charge, the mechanical/thermal load given to the toner and the blade becomes large, so that there occurs such a problem that toner is damaged or deteriorated. Moreover, this arrangement has the following defect: toner which has been softened by frictional heat is fused and adheres to the blade or the developing roller, so that charging property of toner deteriorates and the developing device becomes out of order.
Also in the arrangement in which toner is charged by the friction against the carrier, in order to obtain the sufficient amount of charge, it is required to stir the toner and the blade at a high speed so as to enlarge the speed difference as in the arrangement in which the blade is used. Thus, excessive mechanical/thermal load is given to the toner and the carrier, so that this raises such a problem that toner/carrier is damaged or deteriorated. Moreover, this arrangement has the following defect: toner which has been softened by frictional heat is fused and adheres to the blade or the developing roller, so that charging property of toner deteriorates.
In the developing device using the method which causes toner to come into contact with the charging means such as blade/carrier with a large speed difference maintained (contact charging method), mechanical/thermal load given to the charging means such as toner, and blade/carrier is large.
In particular, toner which requires less fixing energy in accordance with reduction in a softening point of toner, or has higher coloring performance in accordance with increase in a pigment amount of toner (damage-proof property of toner is lowered) has been being improved as an energy-saving technique recently. However, since the conventional friction-charging method gives mechanical/thermal load to toner as described above, it is impossible to apply the method to the above-mentioned toner.
The object of the present invention is to provide (a) a developing device which can reduce mechanical/thermal load given to toner and toner charging means for charging the toner so as to prevent deterioration of toner and the device, (b) a charging method used therefore, and (c) a printing apparatus having the developing device.
Alternately, the object of the present invention is to provide a developing device which can prevent toner from deteriorating, that is, from being damaged and from adhering to a blade so as to improve reliability in developing images, and is particularly to provide (a) toner whose softening point is lowered so as to reduce a fixing energy and (b) a developing device which can be applied to toner whose pigment amount is increased so as to heighten the coloring performance.
In order to achieve the foregoing object, a developing device of the present invention, which is used in an electrophotographic apparatus to develop an electrostatic latent image on a latent image support body by developer that has been charged, includes: transport means for supporting the developer so as to transport the developer to the latent image support body; and charging means which includes (a) an electron inducing section for inducing its electrons by receiving light irradiation and (b) irradiating means for irradiating light to the electron inducing section, and gives the electrons to the developer so as to charge the developer, wherein the charging means and the transport means have a space therebetween, and a grid electrode for controlling a flow of the electrons is provided in the space.
According to the foregoing arrangement, the charging means and the transport means have a space therebetween, so that developer and the charging means are not in contact with each other while having a great speed difference when the developer being transported is charged. Thus, mechanical/thermal load given to the developer and the charging means can be restricted. Thus, it is possible to prevent developer from deteriorating (from being damaged) and the device from deteriorating. Further, it is possible to prevent deterioration in charging property of developer which is brought about since developer softened by frictional heat between the charging means and the transport means adheres to the charging means or the transport means.
Further, the grid electrode is provided, so that it is possible to control a flow of electrons flowing from the charging means to the transport means. Thus, it is possible to restrict dispersion of the charging amount with respect to developer, so that it is possible to stabilize a surface potential of developer at a desired value. Thus, reliability of the developing device can be improved.
Alternately, in order to achieve the foregoing object, the developing device of the present invention, which is used in an electrophotographic apparatus to develop an electrostatic latent image on a latent image support body by developer that has been charged, includes: a developer support body for supporting the developer so as to transport the developer to the latent image support body; and developer charging means for charging the developer, wherein the developer charging means is provided so as to be separated from the developer support body and is provided with an electron emitting section which can emit electrons toward the developer which is to be charged, and the developer charging means charges the developer by sprinkling the electrons, that have been emitted from the electron emitting section, over the developer.
According to the foregoing arrangement, in the developing device, developer can be charged by the developer charging means. In this case, it is not necessary that a layer thickness restricting blade, which restricts a layer thickness of toner provided on the developer support body as a layer, has both functions: (a) a toner-layer-thickness restricting function and (b) a toner charging function, but the layer thickness restricting blade can specialize in the toner-layer-thickness restricting function.
Further, the developer charging means is provided so as to be separated from the developer support body, and the developer charging means charges the developer by sprinkling the electrons, that have been emitted from the electron emitting section, over the developer. That is, the developer charging means can charge developer without giving any load to the developer.
Thus, in the developing device, it is possible to largely reduce pressure of the layer thickness restricting blade exerted on the developer support body compared with a conventional layer thickness restricting blade, so that load (mechanical load and thermal load) exerted on the developer is reduced. Thus, it is possible to prevent developer from being damaged and from adhering.
For a fuller understanding of the nature and advantages of the invention, reference should be made to the ensuing detailed description taken in conjunction with the accompanying drawings.